Elon Musk's Tesla and SpaceX are among a further 31 companies that have jumped on board to support an amicus brief against United States President Donald Trump's executive order banning travel into the United States from seven countries.

The companies have argued that the ban, which prevents travel into the US from Iran, Iraq, Syria, Sudan, Somalia, Yemen, and Libya, is a violation of immigration laws, as well as being discriminatory and preventing US businesses from being able to acquire talent globally.

Filed with the Court of Appeals for the Ninth Circuit, the amicus curiae brief joins the State of Washington v Donald J Trump case.

"Leading technology companies and leading businesses ... are affected by the Executive Order issued on January 27, 2017, entitled 'Protecting the Nation from Foreign Terrorist Entry into the United States'," the brief says.

"The order represents a significant departure from the principles of fairness and predictability that have governed the immigration system of the United States for more than 50 years -- and the order inflicts significant harm on American business, innovation, and growth as a result.

"The order makes it more difficult and expensive for US companies to recruit, hire, and retain some of the world's best employees. It disrupts ongoing business operations. And it threatens companies' ability to attract talent, business, and investment to the United States."

The court is due to hear arguments on Tuesday, after District Judge James L Robart temporarily lifted the travel ban over the weekend -- a decision condemned by Trump.

"The opinion of this so-called judge, which essentially takes law-enforcement away from our country, is ridiculous and will be overturned," Trump wrote in a tweet.

"I have instructed Homeland Security to check people coming into our country VERY CAREFULLY. The courts are making the job very difficult!" he added.

Despite joining the amicus brief, Musk remains on the Trump administration's economic advisory committee -- along with IBM CEO Ginni Rometty, Disney CEO Bob Iger, Pepsi CEO Indra Nooyi, General Motors CEO Mary Barra, and others -- but said this should not be taken as a sign that he agrees with Trump's policies.

"In December, I agreed to join the presidential advisory forum to provide feedback on issues that I think are important for our country and the world. In tomorrow's meeting, I and others will express our objections to the recent executive order on immigration and offer suggestions for changes to the policy," Musk tweeted last week.

"Advisory councils simply provide advice, and attending does not mean that I agree with actions by the administration. My goals are to accelerate the world's transition to sustainable energy and to help make humanity a multi-planet civilisation, a consequence of which will be the creation of hundreds of thousands of jobs and a more inspiring future for all. I understand the perspective of those who object to my attending this meeting, but I believe at this time that engaging on critical issues will on balance serve the greater good."

Musk added that during the first meeting of the committee, he raised the travel ban and "climate" as issues despite them not being on the agenda.

Uber CEO Travis Kalanick resigned from the same advisory committee last week in response to mounting pressure from industry, saying his presence on the panel was "misinterpreted".

"Joining the group was not meant to be an endorsement of the president or his agenda, but unfortunately it has been misinterpreted to be exactly that," Kalanick said.

"There are many ways we will continue to advocate for just change on immigration, but staying on the council was going to get in the way of that."

Last week, Microsoft also filed a formal request to Secretary of Homeland Security John Kelly and Secretary of State Rex Tillerson for an exception to the travel ban, saying visa-holding students and workers who are "responsible known travellers with pressing needs" should be permitted to re-enter the nation under the sponsorship of US companies and universities.

In the letter to Kelly and Tillerson [PDF], Microsoft's president and chief legal officer Brad Smith pointed out that the tech giant has 76 employees, and 41 associated dependents, who have non-immigrant visas allowing them to live and work in the US -- some of whom with "particularly pressing needs" to travel overseas.

"We are concerned about families that have been separated, as one or both parents were outside the United States last Friday and therefore cannot re-enter the country and are stranded away from their homes," Smith wrote.

"We are also concerned about an impacted employee inside the United States with a desperate need to visit a critically ill parent abroad. These situations almost certainly are not unique to our employees and their families. Therefore, we request that you create an exception process to address these and other responsible applications for entry into the country."

According to Microsoft, the ban is counter-productive for US economic growth, as it "creates a significant burden on US companies".

Linux, Red Hat, IBM, Cloud Foundry Foundation, Canonical, and Ubuntu have also opposed the immigration ban, saying that the open-source industry is reliant on the open exchange of ideas across the globe.

"Red Hat and our global economy benefit from immigration laws that both seek to protect the public and recognize that we have diverse backgrounds," Red Hat CEO Jim Whitehurst said in a blog post.

"We are looking carefully at Friday's US executive order on immigration and how it will be implemented. From what we see so far, we are concerned that the changes are inconsistent with Red Hat's values, including diversity.

"Red Hat is strong because of the thousands of diverse voices that comprise our company. Our continued work to advance the technology industry depends greatly on our ability to attract the best and brightest talent from around the world."

Linux executive director Jim Zemlin added that the immigration restrictions are "antithetical to the values of openness and community that have enabled open source to succeed".

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